Photoelectric control unit for oil burners and the like



PHOTOELECT-RIC CONTROL mum FOR OIL BURNERS AND THE LIKE Filed June 13.1956 June 17, 1958 D L I 2,839,130

DONALD ST. CLAIR INVENTOR BY M AGENT United States ast-m i1 5- a gdetail free We a. on.

PHQTOELECTREC CQNTRQL UNiT Fill DEL BURNERS AND THE LHQE Donald St.Clair, St. Albaus, N. Y., assignor to Clair don, Ina, Paterson, N. 3., acorporation of New sersey Application June 13, 1956, Serial No. 591,176

8 Claims. oi. res-2s My present invention relates to a safety controlunit for heating systems, such as oil burners, utilizing a photoelectricscanner as an indicator of proper or improper operation of the system. Aunit of this description has been disclosed in my co-pending applicationSer. No. 577,727, filed April 12, 1956.

it is convenient to use a single photoelectric device to check upon theperformance of both the pilot light and the main burner of a heatingsystem. A difficulty resides, however, in the need for criticallyadjusting and positioning the scanner so that it will respond to therelatively weak pilot light but will not give a false indication inresponse to the infrared afterglow of the heating chamber once the mainburner has been extinguished.

The object of my present invention is to provide means for avoiding theabove difiiculty and enabling the use of a single photoelectric scannereven in such systems where its positioning close to the pilot flame andshielded from the afterglow is not feasible.

Safety control units of the character referred to gener ally comprisesome switching means, such as a relay, arranged to operate near thebeginning of a work cycle of the unit to activate the pilot-lightassembly, under the control of a timer, for a period of sumcientduration to allow the main burner or burners to be ignited. Inaccordance with the present invention 1 provide a sensitivity-controlcircuit for the photoelectric scanner which is adjusted by the timer toa state of increased scanner sensitivity during the period preceding thelighting of the main burner and is restored to a state of normalensitivity at about the time of deactivation of the pilotlight assembly.According to a more particular feature of my invention, the change inscanner sensitivity is brought about by contacts of the relay throughwhich the pilot-light assembly is activated.

The invention will be described in greater detail with reference to theaccompanying drawing whose sole figure is a circuit diagram showing theprincipal elements of a heating system in combination with a safetycontrol unit embodying my present improvement. This figure is similar toFig. 1 of my above'identified copending application and illustrates somuch of my previously disclosed system as is necessary for anunderstanding of the instant invention, the same reference charactershaving been used to designate similar parts. All transformers, auriliaryswitches and other circuit elements not essential for the. presentdisclosure have been omitted, along with the air-circulating systemusual in such installations and shown in myv earlier application.

The boiler Iltl is provided with one or more burners ll supplied withfuel, e. g. i1 by a pump 12 which in turn is driven by a motor M2; alsoincluded in the main fuel line leading to burner 11 is asolenoid-controlled valve S2 and a throttle 17 controlled by a modulator18. A

pilot nozzle 14 is connected by way of a solenoid-controlled valve S1 toa source of fuel (e. g. gas), not shown, and adapted to be lit by anigniter 15. A photoelectric scanner, comprising a tubular shield 16 infront of a photocell PH, is trained upon the burner 11 and the pilotnozzle 14 so as to receive light from any flame appearing thereon.

A source AC of alternating current, which may be the usual utilitymains, is connected across a pair of bus bars and 292, the latter busbar being grounded. For the sake of simplicity all the circuit elementshave been shown to be energizable directly from bus bar 201, although inpractice the voltage to some of these elements may be reduced by meansof step-down transformers as illustrated in my co-pending applicationabove referred to.

The safety control unit associated with the boiler 10 includes aprincipal relay RYl, an auxiliary relay RY2, an igniter control relayRYS, a burner-control relay RY6, a flame-failure relay RY7 and an alarmrelay RY8; a double triode V1 and a thyratron tube V2; a network ofresistors Rib-416 and R8R10, condensers C1-C4 and rectifiers REE, RE2associated with these tubes; a potentiometer P2 to whose slider thecathode of tube V2 is connected; an alarm device schematically indicatedas a lamp AL; and a timer circuit comprising several thermal delayrelays Dill, DRZ, DIM and DRS.

The winding of relay RYIl is connected between bus bars 291 and 262 byway of a conductor 204 and a limit switch LS which is closed by theboiler, in a manner well known per se (e. g. in response to fallingsteam pressure), to send in effect a start signal to the control unitwhenever the system calls for heat. The heating coils of delay relaysDR} and DR4 are normally energized over the armature and back contact ofrelay RYl and over the left-hand armature and back contact of relay RY7,respectively. Relay RYfi, whose winding is bridged by condenser C2, isalso energizable in the closed condition of limit switch LS in a circuitextending from conductor 204 through the normally closed contacts ofdelay relay DRE, right-hand back contact and armature of relay RY7, alead 217, rectifier REl through its winding to ground on bus bar 2&2.Relay RY7 has its winding connected between live bus bar 201 and theplate of thyratron V2 whose cathode is adjustably biased by a voltagedivider composed of potentiometer P2 (bridged by condenser Cd) andresistor R10 in series; this voltage divider is connected between groundon bus bar 202 and a positive direct-current lead 229 which is connectedto conductor 204 via rectifier R52. Lead 220 also extends to the platesto the double triode V1 which are grounded for alternating current bycondenser C1.

The cathode of the right-hand section of tube V1 is connected to groundthrough an individual voltage divider R2, R5 in series with resistor R6which is common to both cathodes of this tube; the cathode of theleft-hand section is connected to ground through its individual voltagedivider R1, R4 in series with resistor R6. The junction between resistorR2, R5 is connected through a large balancing resistor R3 to the commonterminal of resistors R1, R4 and is further connected through resistorR9 and a lead 221 to the grid of thyratron V2 and through aresistance-capacitance network RS, C3 of large time constant toconductor 215 leading to the righthand grid of tube Vl; the left-handgrid of this tube is grounded.

The heating coil of delay relay DRZ and the winding of auxiliary relayRYZ are energizable in parallel over a circuit including the frontcontact and armature of relay RYS, a conductor 223 and the front contactand armature of principal relay RY Relay RYZ has its front contact andarmature connected in series with the make contacts of delay relay DRZbetween conductor 204 and a lead 219 extending toward the right-handfront contact of relay-RY7. Alarm lamp AL is operable in a circuitincluding a conductor 215, back contact and armature of relay RY8, aconductor 223, and the front contact and armature of relay RY1. i

Burner-control relay RY6 has its winding connected between ground busbar 202 and the make contacts of thermal relay DR5 whence extends aconductor 218 to live bus bar 201 via the left-hand front contact andsolenoid S1; an outer left-hand armature of relay RY5 is connected tothe right-hand front contact of relay RY6. The modulator 18 has agrounded input terminal and two ungrounded input terminals HL and HRmarked fast and slow, respectively. Terminal HR is connected via a lead212 to the back contact associated with the right-hand armature of relayRY6 which, like its lefthand armature, is connected to bus bar 201.Terminal BL is connected via a lead 211 to the back contact associatedwith the outer left-hand armature of relay HY 5. Modulator 18 isarranged, in a manner known per se and illustrated in greater detail inmy copending application, to move throttle 17 to wide-open position inresponse to energization of its fast terminal HL and to nearly closedposition in response to energization of its slow terminal HR. The frontcontact associated with the left-hand armature of relay RY6 is connectedvia a lead 209 to the ungrounded input terminals of motor M2 and mainvalve solenoid S2.

Photocell'PH has its anode connected via a lead 214 to the high-voltageterminal of potentiometer P2 at its junction with resistor R10. Inaccordance with the present invention, the cathode of this photocell isconnected to lead 215 (which extends to the right-hand grid of tube V1)not directly, as in my prior application, but through contacts operatedby the ignition-control relay RY5. For this purpose the relay RY5 isprovided with an extra (right-hand) armature which is connected to lead215 and Whose front contact is tied to the photocell cathode via aconductor 115; a potentiometer P is connected between conductor 115 andground, its slider being tied to the back contact of the right-handarmature of relay RY5. Potentiometer P is so adjusted that the normallybalanced amplifier V1 is efiectively unbalanced by the current drawn byphotocell PH when the latter sees the flames of burner 11 but not whenits cathode is excited by spurious infrared radiation from thesurrounding heating chamber; when the potentiometer is bypassed in theactuated condition of relay RY5, the sensitivity of the circuit isincreased so that unbalance occurs in response to the relatively weakflame on pilot nozzle 14.

a The operation of the system illustrated in the drawing will now bedescribed.

Closure of limit switch LS energizes the principal rel-ay RY1 andremoves heating current from thermal relay DR1 whose delay period, asindicated in the drawing, is assumed to be 30 seconds. Relay RY1, inoperating,

also closes a gap in the alarm circuit of device AL but this circuit hasmeanwhile been broken by the energization of relay RY8 in parallel withrelay RYlover the still-closed contacts of delay relay DR1. Theoperation of relay RY8 actuates relay RY2, whose energization is withoutimmediate effect so far as the present disclosure is concerned, andsupplies heating current to the coil of thermal relay DR2 whose delayperiod has been assumed to be seconds.

Current from auxiliary bus bar 204 also flows through the closedcontacts of thermal relay DR4, assumed to have a delay period of 45seconds, and energizes relay RY5. The latter, at its inner left-handarmature, connects bus bar 201 to conductor 208 and, thereby, to igniter15 and pilot valve solenoid S1. If. a flame appears on nozzle 14,. as itshould under normal operating conditions, photocell PHis excited and,after an interval of about one second determined by the time constant ofnetwork R8, C3, drives the right-hand grid 'of amplifier tube V1sutficiently positive to draw a current capable of ionizing thethyratron V2 by raising the potential of the junction 'betweenresistorsR2 and R5 to which the grid of the thyratron isconnected. Relay RY7,which is slow-releasing as indicated, is thus'energized.

The operation of relay RY7 transfers the energizing circuit of relay RY8from the contacts of thermal relay DR1 to those of thermal relay DR2 andauxiliary relay RY2 so that thecircuit of alarm device AL'will remainopen after relay DR1 opens its contacts. Relay RY7 also connects heatingcurrent to thermal relay DR5 whose delay period has been assumed to be-15 seconds. Afterthis period has elapsed, relay DR5 closes its con tactsand operates burner-control relay RY6.

The operation of the last-mentioned relay actuates fuel pump 12 andopens the main valve controlled by solenoid S2. Modulator 18, whichpreviously had operated throttle 17 to nearly closed position by virtueof the potential applied to its slow input HR over the back contact ofrelay RY6, remains in its position since the connection to its fastinput HLis open at the outer left-hand armature of relay RY5. Enoughfuel reaches the burner 11, however, to allow the same to be lighted bythe flameon pilot nozzle 14.

Relay RY7, in operating, also removed heating current from delay relayDR4 so that after 45' seconds the circuit of relay RY5 is broken and thelatter relay releases. de-energized and potentiometer P is againconnectedin the circuit.

If the burner 11 has been properly lit, photocell PH continues tounbalance the amplifier V1 so that thyratron V2 remains ionized andrelay RY7 holds up; Modulator 18 is now operated to move throttle 17 toits wide-open position and burner 11 obtains fuel at maximum rate. L

When the needs of boiler 10 have been satisfied, limit switch LS opensand removes the potential from auxil iary bus bar 204, thereby breakingthe operating circuit of alarm relay RY8, principal relay RY1 and theother fast-acting relays shown. The system then returns to normal.

If at any time in the above-described cycle the photocell PH should havebeen insufliciently energized withv limit switch LS closed and thecontacts of delay relay DR1 opened, the non-operation or release offlametailure relay RY7 would have de-activated alarm relay RY8 andoperated the device AL over the front contact of relay RY1. Suchinsufficient energization would occur it, with potentiometer P in,circuit (relay RY5 unoperated), the flames on burner 11 should go outwhile the boiler still calls for heat, the remaining backgroundradiation being ineifective to excite the scanner PH, V1 in its normalcondition of reduced sensitivity.

It will be appreciated that the specific circuit connec tions shown anddescribed illustrate but one possible mode of realization and that theinvention may be embodied in a variety of modifications, which will bereadily apparent to persons skilled in the art, without departing fromthe spirit and scope of the appended claims. e

I claim:

1. In a heating system, in combination, a burner, fuelsupply means forfeeding fuel to a burner, a pilot nozzle adjacent said burner, ignitermeans for lighting said pilot nozzle, switching means operable'inresponse to the need Igniter 15 and pilot valve solenoid S1 arenow foroperation of the said burner, first relay means operable under thecontrol of said switching means for establishing a first operatingcircuit for the actuation of said igniter means, photoelectric scannermeans positioned to be excited in the lighted condition of said pilotnozzle and of said burner, adjuster means including contacts of saidfirst relay means for adjusting said scanner means to a condition ofrelatively high sensitivity in the operated condition of said firstrelay means and to a condition of relatively low sensitivity in theunoperated condition of said first relay means, timer means responsiveto operation of said switching means for measuring a time intervalsufiicient for the lighting of said pilot nozzle, second relay meanscontrolled by said scanner means for inactivating said first relay meansfollowing the lighting of said pilot nozzle, third relay meanscontrolled by said second relay means for establishing a secondoperating circuit for the actuation of said fuel-supply means, andcircuit-breaker means jointly controlled by said timer means and by saidsecond relay means for inactivating both said first and third relaymeans in the unexcited condition of said scanner means at the end ofsaid time interval.

2. The combination according to claim 1, further comprising an alarmcircuit and fourth relay means jointly controlled by said second relaymeans and by said timer means for closing said alarm circuitsubstantially concurrently with the operation of said circuit-breakermeans.

3. The combination according to claim 1, wherein said timer meanscomprises a principal relay responsive to said signaling means andthermal relay means controlled by said principal relay.

4. The combination according to claim 3, wherein said thermal relaymeans has a delay time of the order of a major fraction of a minute.

5. In a heating system comprising a main burner and a pilot nozzle, incombination, first electrically operable means for lighting said pilotnozzle, second electrically operable means for feeding fuel to saidburner, circuit means for sequentially actuating said first and saidsecond electrically operable means, photoelectric scanner means trainedupon said pilot nozzle and upon said burner, control means responsive tosaid circuit means for maintaining said scanner means at a relativelyhigh level of sensitivity before actuation of said second electricallyoperable means and at a relatively low level of sensitivity thereafter,and delayed-action alarm means controlled by said scanner means and bysaid circuit means for indicating flame failure a predetermined periodafter operation of said first electrically operable means.

6. The combination according to claim 5, wherein said scanner meanscomprises a photocell and an amplifier having an input circuit connectedto be energized from said photocell, said control means includingresistance means in said input circuit and contacts for selectivelyby-passing said resistance means.

7. The combination according to claim 6, wherein said first electricallyoperable means comprises a relay, said contacts being controlled by saidrelay.

8. The combination according to claim 5, wherein said delayed-actionalarm means includes a thermal relay.

References Cited in the file of this patent UNITED STATES PATENTS2,170,497 Gille Aug. 22, 1939 2,388,124 Crews Oct. 30, 1945 2,440,700Rosche May 4, 1948 2,662,591 Hanson Dec. 15, 1953

